1. Field of the Invention
The present invention is related generally to implantable orthopedic implants. More specifically, the present invention is related to implantable orthopedic bone plates used to reinforce fractured bones.
2. Prior Art
Orthopedic bone plates play a critical role in the healing process of broken bones. Once a bone has been fragmented, it is ideal for the broken bone fragments to be joined back together under compression to promote improved healing. The bone plate is a critical device that is used as a stabilizing bar to bridge the gap between bone fragments.
During surgery, a bone plate is inserted next to the fragmented bone of a patient. Compression screws are first placed through the bone plate. They are anchored into each of the bone fragments and tightened, pulling the bone fragments together under a compression load and against the plate. Once the compression screws are set in place, locking bone screws are inserted through the bone plate and anchored into the fragmented bone. The locking screws in conjunction with the bone plate secure the bone fragments together and the compression created by the compression screws ensures that they do not move. However, high tensile stresses are created when the bone fragments are fixated with the locking screws. These tensile stresses could damage the fragile bone fragments and impair the healing process. Bone plates, therefore, are a key element in the bone healing process.
Bone fragmentation, however, is unpredictable. As a result of a traumatic experience, a bone may fragment in multiple erratic locations and present itself in random orientations. Every patient's bones are unique; no two bones will fragment in the same manner in the same orientation. Nevertheless, traditional bone plate technology makes it difficult for a bone plate to be oriented in such a manner as to be utilized correctly for every trauma situation. Bone plates are rigid braces, typically composed of metal, which have historically been designed with fixed threaded holes through which some bone screws may not properly align with the matching bone fragment. In that respect, early bone plate technology comprised bone plates with preexisting threaded holes in combination with threaded locking screws. These earlier bone plates often lacked the ability to secure bone fragments that were not aligned under the threaded screw holes. That is because the preexisting threaded holes of earlier bone plate technology confined the angle through which the locking screw could be advanced into a bone fragment.
For example, with the earlier bone plate and screw technology, the physician could only advance the screw along the pre-defined orientation of the threads in the bone plate. This limitation often created a problem for the physician in that only bone fragments that presented themselves directly under a threaded aperture in the bone plate could be secured together. Examples of these earlier bone plate and locking screw devices are disclosed in U.S. Pat. No. 5,709,686 to Talus et al.; U.S. Pat. No. 6,206,881 to Frigg et al.; and U.S. Pat. No. 6,306,140 to Siddiqui, the disclosures of which are incorporated herein by reference.
In an effort to increase the degree of freedom in healing fractured bones, bone plates were developed with locking screws that can be inserted at different angles through the plate. One such improvement was the development of a bone plate with a tappable contact region as disclosed in U.S. Pat. No. 6,955,677 by Dahners. The disclosure of this patent is incorporated herein by reference. The '677 patent discloses a bone screw with a threaded head that is intended to penetrate into the hole of the bone plate in a tapping fashion. A drawback to this invention, however, is that it utilizes a softer bone plate material which lacks rigidity and stiffness to bear high tensile loads. Over time the softer material of the bone plate can yield to tensile stresses, resulting in possible movement of the bone fragments, which is detrimental to proper healing of the bone fragments.
Accordingly, an orthopedic device is needed that expands the possible locking screw insertion angles in anchoring bone fragments to promote bone healing.